[python-control-discuss] NoneType and circular relative imports

[Dale L. P. <haz...@gm...>]

In src/lti.py, NoneType is being imported and used in the Lti class in
two locations.  Is there a reason this can't be just None?  NoneType
is deprecated in Python3 and this is causing issues for me.

Also, I am getting this import error when I import control:
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
<ipython-input-1-4964879682bf> in <module>()
----> 1 import control

/home/hazelnusse/usr/lib64/python3.2/site-packages/control-0.6a-py3.2.egg/control/__init__.py
in <module>()
     58 # Import functions from within the control system library
     59 #! Should probably only import the exact functions we use...
---> 60 from .bdalg import series, parallel, negate, feedback
     61 from .delay import pade
     62 from .dtime import sample_system

/home/hazelnusse/usr/lib64/python3.2/site-packages/control-0.6a-py3.2.egg/control/bdalg.py
in <module>()
     53
     54 import scipy as sp
---> 55 from . import xferfcn as tf
     56 from . import statesp as ss
     57

/home/hazelnusse/usr/lib64/python3.2/site-packages/control-0.6a-py3.2.egg/control/xferfcn.py
in <module>()
     82 from .lti import Lti, timebaseEqual, timebase, isdtime
     83 from warnings import warn
---> 84 from . import statesp
     85
     86 class TransferFunction(Lti):

/home/hazelnusse/usr/lib64/python3.2/site-packages/control-0.6a-py3.2.egg/control/statesp.py
in <module>()
     83 import warnings
     84 from .lti import Lti, timebaseEqual, isdtime
---> 85 from . import xferfcn
     86
     87 class StateSpace(Lti):

ImportError: cannot import name xferfcn

I noticed that xferfcn.py has:
from . import statesp

and that statesp.py has:
from . import xferfcn

I am guessing is a circular dependency issue.  From what I can tell,
each of these modules only imports these to do some type checking of
arguments.

Luke


-- 
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